From 31e22a220a9b81dfc13ead45da800e97f9de02c9 Mon Sep 17 00:00:00 2001
From: Arturs Artamonovs <dos21h@gmail.com>
Date: Sun, 26 Nov 2023 08:22:42 +0000
Subject: Add last part of procfs notes

---
 md/notes/kernel/create_procfs_entry.md | 125 +++++++++++++++++++++++++++++++--
 1 file changed, 121 insertions(+), 4 deletions(-)

diff --git a/md/notes/kernel/create_procfs_entry.md b/md/notes/kernel/create_procfs_entry.md
index 03d186f..dcb51c8 100644
--- a/md/notes/kernel/create_procfs_entry.md
+++ b/md/notes/kernel/create_procfs_entry.md
@@ -112,8 +112,56 @@ void procfs_entry_exit( void )
 }
 ```
 
-Next step add data to read from file entry
+Now module can be run and there is one file under the /proc/secret
 
+Next step add data to read from file entry/
+
+Update the file operation functions, so its possible to read some data from /proc/secret/file
+
+```c
+char file_data[256] = "This is data\n";
+static int read_once=1;
+
+
+static int secret_open(struct inode *inode, struct file *file) {
+        return 0;
+}
+
+static int secret_release(struct inode *inode, struct file *file) {
+        return 0;
+}
+
+static ssize_t secret_read(struct file *file, char __user *buffer, size_t length, loff_t *offset) {
+       int len=0;
+       if (read_once) {
+               read_once=0;
+       } else {
+               read_once=1;
+               return 0;
+       }
+       len = strlen(file_data);
+       if (copy_to_user(buffer, &file_data, len)) {
+               pr_err("secreate_read: Error\n");
+       }
+       return len;
+}
+
+static ssize_t secret_write(struct file *file, const char *buffer, size_t length, loff_t *offset) {
+        return 0;
+}
+```
+
+Now some data is exposed if module is loaded and run command
+
+```sh
+cat /proc/secret/file
+```
+
+output will be
+
+```sh
+This is data
+```
 
 
 
@@ -127,12 +175,81 @@ Next step add data to read from file entry
 
 ## Final result
 
-__Makefile__
-```Makefile
-```
 
 __procfs_entry.c__
 ```c
+#include <linux/module.h>  /* Needed by all modules */
+#include <linux/kernel.h>
+#include <linux/proc_fs.h>
+
+static struct proc_dir_entry *procdir, *procfile;
+char file_data[256] = "This is data\n";
+static int read_once=1;
+
+static int secret_open(struct inode *inode, struct file *file) {
+	return 0;
+}
+
+static int secret_release(struct inode *inode, struct file *file) {
+	return 0;
+}
+
+static ssize_t secret_read(struct file *file, char __user *buffer, size_t length, loff_t *offset) {
+        int len=0;
+	if (read_once) {
+		read_once=0;
+	} else {
+		read_once=1;
+		return 0;
+	}
+	len = strlen(file_data);
+	if (copy_to_user(buffer, &file_data, len)) {
+		pr_err("secreate_read: Error\n");
+	}
+	return len;
+}
+
+static ssize_t secret_write(struct file *file, const char *buffer, size_t length, loff_t *offset) {
+	return 0;
+}
+
+static struct proc_ops procfs_ops = {
+        .proc_open = secret_open,
+        .proc_read = secret_read,
+        .proc_write = secret_write,
+        .proc_release = secret_release
+};
+
+
+int procfs_entry_init( void )
+{
+	printk(KERN_DEBUG "Hello Procfs!\n");
+	procdir = proc_mkdir("secret", NULL);
+	if (procdir == NULL) {
+		pr_err("Cant create secret directory\n");
+		return -1;
+	}
+
+	procfile = proc_create("file", 0644, procdir, &procfs_ops);
+	if (procfile == NULL) {
+		pr_err("Cant create file under the secret\n");
+		return -1;
+	}
+
+	return 0;
+}
+
+void procfs_entry_exit( void )
+{
+	printk(KERN_DEBUG "Exit Procfs!\n");
+	proc_remove(procdir);
+	proc_remove(procfile);
+}
+
+module_init( procfs_entry_init );
+module_exit( procfs_entry_exit );
+
+MODULE_LICENSE("GPL")
 ```
 
 ## Links
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